In a typical irrigation apparatus, an elongated main pipe or line has a plurality of large support wheels fixed thereto along its length. The irrigation line also includes a plurality of sprinkler heads positioned at intervals there along. In a typical use of the device, water under pressure is supplied to the main pipe, exiting through the sprinkle heads along the length of the main pipe, with the pipe remaining in a fixed position relative to the ground. When the area of ground adjacent the apparatus is sufficiently irrigated, turning force is applied to the main pipe to rotate it about its longitudinal axis, so that the wheels in turn rotate, whereby the apparatus may be moved to a new location. During such movement, water under pressure is not supplied to the apparatus, so that no irrigation during this line movement takes place.
Upon arrival of the apparatus in another area to be irrigated, the apparatus is stopped in a position wherein each sprinkler head is substantially erect, so that the operation of the sprinkler heads will be in accordance with the desires of the operator. In the case wherein the sprinkler heads are rigidly fixed to the main pipe, a certain amount of time-consuming alignment is necessary to achieve this. The problem is made more difficult by the very considerable length of main pipe and the possibility of torsional displacement of portions of the pipe relative to each other, or due to the unevenness of the ground upon which the wheels rest.
Irrigation systems which include provision for self-erecting sprinklers are known (for example, U.S. Pat. No. 3,002,697 to Jones, U.S. Pat. No. 3,045,922 to Jensen, U.S. Pat. No. 3,090,566 to Snyder et al, and U.S. Pat. No. 3,143,298 to Jones). In these patents, each pivotal structure is raised sufficiently from the main line to allow the entire pivotal structure to clear the main line as it swings. Additionally, in these patents, the center of gravity of each pivotal structure is not directly below the weight-bearing pivotal connection of the pivotal structure. Thus, a cantilevered support of the weight is in effect.
An additional problem occurring in the type of system having sprinkler heads rigidly secured to a main line is that, even with initial, proper, erect positioning of the sprinkler heads, no provision is made for wind which disturbs the pattern of irrigation in an undersirable way.